Push-pull attachment for lift trucks

ABSTRACT

A novel lazy tongs has offset pivotal connections between the arms of the linkage allowing the arms to fold together compactly in vertical positions. The lazy tongs linkage actuates a push frame for pushing a load off the forks of the lift truck. An adjustable length connection between the upper forward arm and the push frame allows the upper end of the push frame to be tilted backward in extended position of the linkage so that the thrust may be applied principally at the bottom of the load. Since the adjustable length arm is vertical in retracted position, the push frame is always vertical in retracted position regardless of its tilt in extended position. The rearward tilt of the push frame in extended position is also advantageous in grasping sheetlike pallets to pull a pallet load onto the forks of the truck. The lower edge of the push frame may be equipped with pallet grippers for this purpose.

0 United States Patent [151 3,640,414

Brudi 1 Feb. 8, 1972 [54] PUSH-PULL ATTACHMENT FOR LIFT PrimaryExaminerAlbert J. Makay TRUCKS A!t0rney-Lee R. Schermerhorn [72]inventor: Ronald A. Brudi, Longview, Wash. [57] ABSTRACT Assignee: BruinEquipment, -i Longview, wash- A novel lazy tongs has offset pivotalconnections between the [22] Filed: Man 2 1970 arms of the linkageallowing the anus to fold together compactly in vertical positions. Thelazy tongs linkage actuates a l PP 15,335 push frame for pushing a loadOR the forks of the lift truck. An adjustable length connection betweenthe upper forward arm and the push frame allows the upper end of thepush frame to '8 gg'gg zgg be tilted backward in extended position ofthe linkage so that [58] Field of Search ..21 1/s2 5 t 516 730 731- mustmy bf app'ied p'imipally {he 25 1 Since the adjustable length arm isvertical in retracted position, the push frame is always vertical inretracted position regardless of its tilt in extended position. Therearward tilt of the [56] References Cited push frame in extendedposition is also advantageous in grasp- UNITED STATES PATENTS ingsheetlike pallets to pull a pallet load onto the forks of the truck. Thelower edge of the push frame may be equipped with 2,616,578 11/1952Dunham ..214 514 x pallet grippers f this purpose 3,151,755 10/1964Quayle ..214/670 6 Claims, 4 Drawing Figures PATEMEDFEB 81972 3540 114SHEET 1 OF 2 INVENTOR. g RONALD A. BRUDI flfiorney PATENIEUFEB 819723.640.414

SHEET 2 BF 2 INVENTOR. RONALD A. BRUDi PUSH-PULL ATTACHMENT FOR LIFTTRUCKS BACKGROUND OF THE INVENTION This invention relates to an improvedpush-pull attachment for lift trucks and has particular reference to animproved lazy tongs linkage for tilting a push frame backward inpushinga load off the forks of the truck and in grasping a sheetlike pallet topull a load onto the forks.

In pushing a load off the forks of a lift truck it is often desirable toapply the major thrust at the bottom of the load in order to avoidpushing the top of the load forward out of vertical alignment,especially when the load is of a deformable nature such as stack ofboxes or the like. On the other hand, it is not desirable to mount thepush frame in a permanently backward tilted position because then thepush frame will not retract compactly against the back of the fork liftcarriage. Compact folding of the pusher linkage is essential in order toposition the load as close to the front wheels of the truck as possiblein carrying and lifting the load. When the push frame is not retractedcompactly against the back of the lift carriage, the center of gravityof the load is located farther forward from the wheels causing the truckto overbalance and thereby reducing the carrying capacity of the truck.For this reason it has heretofore been considered impractical to tiltthe push frame backward, with the result that the top of the load isfrequently pushed forward out of vertical alignment, particularly if themast and forks of the truck are tilted slightly forward when the load isdischarged.

A similar problem arises in pulling a load onto the forks of the truckby means of a sheetlike pallet. In order to adapt a lift truck for theuse of sheetlike pallets, a gripper is mounted at the lower edge of thepush frame to grasp a protruding edge of the pallet sheet. To performthis manipulation, it is usually necessary to tilt the mast of the truckforward in order to place the grippers within an inch or so of thefloor. But when the mast is tilted forward, a normally vertical pushframe is also tilted forward, causing the upper end of the push frame toencounter the load before the grippers are close enoughto the bottom ofthe load to grasp the pallet sheet. This makes it quite difficult to usesheetlike pallets with a conventional lift truck notwithstanding thegreat advantage of such pallets for handling certain types ofmerchandise.

Objects of the invention are, therefore, to provide an improvedextending and retracting mechanism for tilting the push frame on a lifttruck in extended position without any sacrifice of space in retractedposition, to provide means for tilting the push frame backward whenextended and then returning the push frame to vertical position whenretracted, to provide an improved lazy tongs linkage for such purposeand to provide a push-pull mechanism which is better adapted to handlesheetlike pallets.

SUMMARY OF THE INVENTION According to the present invention, the pushframe is extended and retracted by a pair of vertical lazy tong linkageson opposite sides of the lift carriage. The pivotal connections betweenthe arms of each lazy tongs are offset so that all the arms foldcompactly in vertical positions when the push frame is retracted. Theupper forward arm of each lazy tongs is pro vided with a lengthadjustment adjacent a sliding connection with the upper part of the pushframe. By means of this length adjustment the push frame may be causedto assume a conventional vertical position when fully extended or it maybe caused to tilt backward so that the principal thrust in discharging aload from the lift forks is applied at the bottom of the load. Since theadjustable length arms are vertical when fully retracted, this lengthadjustment does not disturb the vertical position of the push frame inretracted position. Thus, regardless of the tilt of the push frame whenextended, it always returns to compact vertical position when retracted.

A backward tilting push frame is especially advantageous in pulling aload onto the lift forks by means of a sheetlike pallet. A backward tiltof the push frame places the pallet grippers at the lower edge of thepush frame close to the bottom of the load even when the mast is tiltedforward to place the grippers and the forward ends of the forks as closeto floor level as possible. The tilt adjustment of the push framethereby provides a two-fold advantage in the use of lift trucks equippedwith the invention.

The invention will be better understood and additional objects andadvantages will become apparent from the following description of thepreferred embodiment illustrated in the accompanying drawings. Variouschanges may be made in the details of construction and arrangement ofparts and certain features may be used without others. All suchmodifications within the scope of the appended claims are includes inthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view withparts broken away, showing a lift truck embodying the invention whereinthe push frame mechanism is extended to grasp a sheetlike pallet;

FIG. 2 is a view on the line 2-2 in FIG. 1;

FIG. 3 is a view similar to FIG. 1 but with the push frame retracted;and

FIG. 4 is a front elevation view of FIG. 3 with parts broken away.

DESCRIPTION OF THE PREFERRED EMBODIMENT The numeral 10 designatesgenerally a conventional lift truck having front wheels 1 1 and a mastl2 and equipped with a cylinder and piston rod 9 for tilting the mast.As shown in FIG. 1, the mast is tilted forward through a small angle 13with respect to vertical line 14. As is understood by persons skilled inthe art, the mast may be moved to vertical position 14 and it may alsobe tilted backward behind vertical line 14 for carrying and lifting aload.

The load is carried on forwardly extending forks 15 on a lift carriage16 which moves vertically on mast 12. In most cases the mast 12 is anextension type of mast having telescoping, vertically sliding sectionswhich may be raised to considerable height for the purpose of stackingand unstacking merchandise or other objects. In FIG. 1, carriage 16 isin its lowermost position whereby the forward tilt of the mast causesthe front ends of forks 15 to be depressed to the floor level 17.

The invention resides in a novel and improved lazy tongs linkage 20 forextending and retracting a vertical or near vertical push frame 21 whichis arranged to push a load 22 off the forks 15. Push frame 21 issupported at its opposite sides by a pair of the lazy tongs 20, one oneach side of the truck. The lazy tongs, in turn, are supported by avertical frame 25 on the lift carriage 16. I

Each lazy tongs linkage comprises four arms 31, 32, 33 and 34. Arms 31and 32 are pivotally connected together intermediate their ends by pins35, and arms 33 and 34 are pivotally connected together intermediatetheir ends by pins 36. The forward end of arm 31 is pivotally connectedto the rear end of arm 33 by a pin 37, and the forward end of arm 32 ispivotally connected to the rear end of arm 34 by pin 38.

Pin 37 passes through a central tongue 40 on arm 33 and a pair of ears41 on arm 31 which straddle the tongue 40. Similarly, the pin 38 passesthrough a central tongue 42 on the arm 32 and a pair of ears 43 on thearm 34 which straddle the tongue 42. Arms 31 and 33 are disposed in acommon vertical plane and arms 32 and 34 are disposed in a commonvertical plane alongside arms 31 and 33.

Pins 37 and 38 are offset relative to the arms so that the axis of pin37 lies in the plane of an underneath flat side 44 of ann 31 and also inthe plane of an undemeath flat side 45 of arm 33. Similarly, the axis ofpin 38 is offset so that it lies in the plane of an upper flat side 46on arm 32 and an upper flat side 47 on arm 34. Thus, the lazy tongslinkage is adapted to fold compactly together as shown in FIG. 3 withflat surface 45 lying against flat surface 44 and flat surface 47 lyingagainst flat surface 46, all of these surfaces being disposed in acommon transverse plane parallel with the planes of supporting frame 25and mast 12. This compact folding feature is of particular advantagewhen lift carriage 16 is equipped with a side shifting mechanism whichoccupies some additional space between the mast and the load, spacingthe load farther forward from wheels 11.

The rear end of arm 31 is pivotally mounted on a pin 49 in the lower endof a vertical channel track 50 mounted on frame 25. The rear end of arm32 is equipped with a roller 51 which rides in the channel track.Similarly, the front end of am 33 pivots on a pin 52 in the lower end ofa vertical channel track 55 on push frame 21 and the front end of arm 34carries a roller 56 which travels in the channel track.

The linkage geometry is such that .pins 37 and 38 always remain in acommon transverse plane parallel with channel track 50, but the lengthof arm 34 is adjustable so that push frame 21 in extended position maybe made parallel to frame 25 or tilted relative thereto as desired. Theforward ends of arms 34 in the two lazy tongs are stabilized by aslightly offset transverse tie rod 57.

Any suitable form of length adjustment may be provided for the arms 34,a preferred embodiment being illustrated in FIG. 2. Roller 56 is mountedon a bar 60 which telescopes in hollow arm 34. Bar 60 is provided with aseries of tapped holes 61 to receive cap screws 62 in selected holes 63in arm 34.

When bar 60 is adjusted to make arm 34 the same effective length as arm33, push frame 21 will remain parallel to the plane of support frame 35in all positions of the lazy tongs linkage. By adjusting bar 60 toshorten the effective length of arm 34 it will be apparent that pushframe 21 in extended position may be tilted backward relative to supportframe 25 as shown in FIG. 1. However, when the linkage is folded to itsFIG. 3 position both arms 33 and 34 become parallel with support frame25 and a transverse plane through the axes of pin 52 and roller 56 isparallel with frame 25. Hence, in fully retracted position, push frame21 is always parallel with support frame 25 regardless of the lengthadjustment of arm 34 because any variation in length merely shifts theroller 56 up or down parallel with frame 25.

In order to handle sheetlike pallets 70, the lower end of push frame 21is equipped with a lower stationary clamp jaw 71 extending across thewidth of the push frame. An upper clamp jaw 72 is actuated by pistonrods 73 in one or more fluid pressure cylinders 74.

In approaching a load 22 on a pallet sheet 70, the mast 12 may be tiltedforward to cause lower clamp jaw 71 to pass under an upfolded edge onthe pallet sheet 70 as shown in FIG. 1. Then by causing claim jaw 72 togrip the pallet sheet, the load may be drawn onto forks by operation ofa fluid pressure cylinder 80 in each lazy tongs. When push frame 21cannot be tilted back to vertical position as shown, the upper end ofthe forward tilted push frame encounters the side of load 22 before theclamp jaws are close enough to grasp the pallet sheet.

One end of cylinder 80 is connected to pivot 52 and a piston rod 81extending from the opposite end of the cylinder is pivotally connectedto a pin 82 in the arm 31. Drawing piston rod 81 into the cylinder foldsthe lazy tong linkage into its FIG. 3 position and pulls the load ontothe forks 15. Extension of piston rod 81 from cylinder 80 causes pushframe 21 to push the load off the forks 15.

By appropriate length adjustment of the arms 34 of the two lazy tongsthe thrust exerted by the two piston rods 81 will be applied to thelower part of the load, even though the mast 12 is tilted forward asshown in FIG. 1. The connection of cylinder 80 directly to pin 52 isadvantageous in providing direct thrust against the lower portion ofpush frame 21 and thereby minimizing stress on the linkage. This permitsa lightweight construction of the linkage amts which also makes for acompact assemblage when folded. Similarly, in pulling the load ontoforks 15, the pull is exerted on pin 52, close to clamp jaws 71 and 72,minimizing stress on the linkage.

Clamp jaws 71 and 72 may be omitted when elevated pallets are usedinstead of sheetlike pallets.

FIG. 3 illustrates the necessity for compact folding of the lazy tongslinkage. Dimension indicates the space occupied by the push frameattachment in front of the back plate of lift carriage 16. Dimension 91indicates the distance of the lift carriage back plate ahead of thefront wheel axis. The sum of these two dimensions is equal to dimension92 which measures the distance from the wheel axis to the back side ofthe load. It will be apparent that any reduction in dimension 90 placesthe center of gravity of the load that much closer to the wheel axis,thereby increasing the load which the truck may safely carry withoutdanger of overbalancing.

I claim:

1. In a lift truck having a load carriage mounted for vertical movementon a mast, a push frame for pushing a load off said carriage, and a pairof lazy tongs on opposite sides of said carriage for operating said pushframe, each of said lazy tongs having an arm pivotally connected to alower portion of said push frame and an arm movable in a vertical guidein said push frame above said pivotal connection, said last arm being astraight, rigid unitary member of a length to tilt said push framebackward as the push frame is extended, said two arms folding into sideby side positions parallel with each other and parallel with said mastwhen the push frame is retracted, causing said push frame to retract toa position parallel with said mast regardless of the length of said lastarm.

2. The invention of claim 1 including a length adjustment in said lastarm to vary the angle of tilt of said push frame in extended position.

3. The invention of claim 1, said lazy tongs having four arms connectedtogether in pairs on offset pivots causing pairs of the arms to lie flatagainst each other in a common transverse plane of contact parallel withsaid mast, whereby said push frame is retracted to a position parallelwith said mast regardless of its angle of tilt in extended position.

4. The invention of claim 1 including a cylinder and piston unit havingone end connected with said pivotal connection on said push frame andits opposite end connected with an arm of said lazy tongs.

5. The invention of claim 1 including pallet clamp means on the lowerend of said push frame for pulling a sheetlike pallet onto said loadcarriages when said push frame is retracted.

6. In a lift truck having a load carriage mounted for vertical movementon a mast, a push frame for pushing a load off said carriage, a pair oflazy tongs on opposite sides of said carriage for operating said pushframe, each of said lazy tongs having four arms connected together inpairs on offset pivots causing pairs of the arms to lie flat againsteach other in a common transverse plane of contact parallel with saidmast, one of said arms being pivotally connected to a lower portion ofsaid push frame and another of said arms being movable in a verticalguide above said pivotal connection, said last arm consisting of twoparts which are adjustable relative to each other to either lengthen orshorten the arm to tilt said push frame either forward or backward inthe extended position of the lazy tongs, and a cylinder and piston unithaving one end connected with said pivotal connection on said push frameand its opposite end connected with an arm of said lazy tongs forextending and retracting said push frame.

* i i i

1. In a lift truck having a load carriage mounted for vertical movementon a mast, a push frame for pushing a load off said carriage, and a pairof lazy tongs on opposite sides of said carriage for operating said pushframe, each of said lazy tongs having an arm pivotally connected to alower portion of said push frame and an arm movable in a vertical guidein said push frame above said pivotal connection, said last arm being astraight, rigid unitary member of a length to tilt said push framebackward as the push frame is extended, said two arms folding into sideby side positions parallel with each other and parallel with said mastwhen the push frame is retracted, causing said push frame to retract toa position parallel with said mast regardless of the length of said lastarm.
 2. The invention of claim 1 including a length adjustment in saidlast arm to vary the angle of tilt of said push frame in extendedposition.
 3. The invention of claim 1, said lazy tongs having four armsconnected together in pairs on offset pivots causing pairs of the armsto lie flat against each other in a common transverse plane of contactparallel with said mast, whereby said push frame is retracted to aposition parallel with said mast regardless of its angle of tilt inextended position.
 4. The invention of claim 1 including a cylinder andpiston unit having one end connected with said pivotal connection onsaid push frame and its opposite end connected with an arm of said lazytongs.
 5. The invention of claim 1 including pallet clamp means on thelower end of said push frame for pulling a sheEtlike pallet onto saidload carriages when said push frame is retracted.
 6. In a lift truckhaving a load carriage mounted for vertical movement on a mast, a pushframe for pushing a load off said carriage, a pair of lazy tongs onopposite sides of said carriage for operating said push frame, each ofsaid lazy tongs having four arms connected together in pairs on offsetpivots causing pairs of the arms to lie flat against each other in acommon transverse plane of contact parallel with said mast, one of saidarms being pivotally connected to a lower portion of said push frame andanother of said arms being movable in a vertical guide above saidpivotal connection, said last arm consisting of two parts which areadjustable relative to each other to either lengthen or shorten the armto tilt said push frame either forward or backward in the extendedposition of the lazy tongs, and a cylinder and piston unit having oneend connected with said pivotal connection on said push frame and itsopposite end connected with an arm of said lazy tongs for extending andretracting said push frame.